Compared with patients with no tobacco smoke exposure, smokers needed 38% more propofol to induce anesthesia, and passive smokers needed 18% more, reported lead investigator Erdogan Ozturk, MD, of Bezmialem Vakif University in Istanbul, and colleagues.
“A limited number of studies exist indicating that smoking increases anesthetic requirements; however, anesthetic agent requirements for individuals exposed to environmental tobacco smoke (passive smokers) have not been studied at all,” the investigators wrote.
Ninety women undergoing total abdominal hysterectomy were enrolled in the study. They were divided into three groups of 30 each based on smoking status: smokers, passive smokers, and nonsmokers. (Nonsmokers had no history of smoking or environmental tobacco smoke exposure).
Smoking status was confirmed by measuring serum cotinine, a metabolite of nicotine and marker of tobacco smoke exposure.
Standard total intravenous anesthesia was performed on all patients. Bispectral index values were maintained at 40-60. After each operation, the investigators assessed the total amounts of propofol and the painkiller remifentanil used.
The average amount of propofol used to induce anesthesia was 102.76 mg for smokers, 84.53 mg for passive smokers, and 63.17 mg for nonsmokers. Smokers needed 38% more propofol than nonsmokers and 17% more than passive smokers to induce anesthesia. Passive smokers needed 18% more propofol than nonsmokers. (P<0.05 for all.)
Total propofol usage for the entire procedure was 179.38 mg for smokers, 150.50 mg for passive smokers, and 119.37 mg for nonsmokers. Smokers used 33% more anesthesia than nonsmokers and 16% more than passive smokers. Passive smokers used 20% more anesthesia than nonsmokers. (P<0.05 for all.)
Total amounts of remifentanil used were 1,315 mcg for smokers, 1,241 mcg for passive smokers, and 1,010 mcg for nonsmokers. Smokers used 23% more of this painkiller than nonsmokers and 6% more than passive smokers. Passive smokers used 18% more than nonsmokers. (P<0.05 for smokers versus nonsmokers.)
“We concluded that the amount of the anesthetic and analgesic required to ensure equal anesthetic depth in similar surgeries was higher in active smokers and passive smokers compared to nonsmokers,” the researchers concluded.
One potential explanation for the results is that nicotine affects the metabolism of anesthetic drugs in the liver. “Our starting point was the idea that cigarettes, which contain more than 4,000 chemicals, may affect drug metabolism,” Ozturk told MedPage Today via email.
“I suggest that healthcare professionals should consider the effect of smoking in their research and plan customized treatment options for each individual. This will optimize the medication process and contribute to the reduction of health expenditures,” Ozturk said.
Because so few studies have explored the question, anesthesiologists generally aren’t aware that smokers may need more anesthesia during surgery, Richard Dutton, MD, an anesthesiologist at the University of Chicago and Chief Quality Officer for the American Society of Anesthesiologists, said in an interview with MedPage Today. Dutton was not involved in the study.
“This is a surprise,” Dutton said. “It’s not something I would have predicted, but I am inclined to believe the results. I would love to see it replicated in a larger study population.”
“It’s biologically plausible. Cigarette smoke is a brain stimulant, and a patient on stimulants needs more anesthesia to get to sleep,” Dutton said.
There is normally 10% to 20% individual variation in the amount of anesthesia patients require, so the 38% difference between smokers and nonsmokers for inducing anesthesia is substantial, Dutton said.
In addition, the fact that smoking status was objectively ascertained by measuring cotinine, rather than relying on self-reports, is an important strength of the study Dutton said.
“If this is borne out by other studies, it could affect clinical practice,” Dutton said. “We should probably be aware that smokers might require more anesthesia.”